The present invention relates to a pressure sensor utilizing a magnetostriction effect of an amorphous magnetic alloy.
Recently, a pressure sensor utilizing a magnetostriction effect of an amorphous magnetic alloy has been proposed, as disclosed in Japanese Patent Unexamined Publication No. 59-111033 (A) for instance.
FIG. 12 is a schematic sectional view of an example of such a conventional pressure sensor.
With reference to FIG. 12, reference numeral 71 denotes a columnar body made of a soft magnetic material, in which an annular groove 71a is formed. On the columnar body 71 there are disposed an amorphous magnetic alloy disc 72 capable of exhibiting magnetostriction and a non-magnetic amorphous alloy spacer 73. A cover 74 equipped with an O-ring 75, in which through-holes 76 are formed, has a hollow portion acting as a pressure introducing opening 74a. A coil 78 is located in the annular groove 71a. All of these members are received in a receptacle 77. Reference numeral 79 denotes a detector unit.
A pressure applied through the pressure introducing opening 74a transmits to the through-hole 76 and push down the amorphous magnetic alloy disc 72, so that a stress is applied onto the amorphous magnetic alloy disc 72. The stress changes a permeability of the amorphous magnetic alloy because of magnetostriction. The change of the permeability is detected as the change in an inductance of the coil 78, to measure the magnitude of the applied pressure by the detection circuit 79.
The amorphous magnetic alloy used in the pressure sensor as afore-mentioned was uneven in thickness and inferior in flatness. Consequently, in the conventional pressure sensor using a thin strip of an amorphous magnetic alloy, the deformation of the thin strip at the time of applying a pressure is suppressed by friction between the thin strip and the spacer. Thereby, the conventional pressure sensor produces such an output characteristics as shown in FIG. 13. With reference to FIG. 13, there is noticed a hysteresis, i.e. a characteristic curve in case of applying a pressure and a characteristic curve in case of reducing an applied pressure from a pressed state are different from each other. Besides, the output voltage characteristics is inferior in linearly, too.
FIG. 14 shows the influence of a temperature on the output voltage of the conventional pressure sensor held under a constant pressure condition. In FIG. 14, it should be noted that the output voltage of the pressure sensor is changed in response to the rising of the temperature.
As afore-mentioned, the conventional pressure sensor was disadvantageous disadvantage because of the change in the output depending on the temperature, and the presence of hysteresis caused by the uneven thickness of the amorphous magnetic alloy, and because its output was inferior in linearity.